The research to be pursued under this proposal deals with two areas of protein X-ray crystallography that have not yet been extensively studied, and which loom to be important in the near future: 1) the study of the general chemical and biochemical expression of functionality of an enzyme molecule using X-ray crystallographic methods, and 2) the problem of refining the structures of two or more slightly different molecules or subunits per asymmetric unit of a crystal. We have been working in the first of these areas for a number of years studying a wide range of chemical and biochemical behavior of alpha-chymotrypsin (alpha-CHT) and not simply restricting ourselves to study of the active site and catalytic properties of the molecule. This has led to the structure determination of over 30 derivatives of alpha- CHT at 2.8A resolution. The results of this work have indicated or suggested the study of other promising classes of behavior which we would like to investigate under this proposal. We have also been working with the problem of two molecules per asymmetric unit since the onset of our structure determination of alpha-CHT. Since about 10 enzyme structure determinations now at various stages of completion fall into this category, we would like to complete our original work on the structure of the dimer by developing fairly routine and reliable methods of dealing with the smaller differences in structure which apparently accompany multiple occupancy in the asymmetric unit. Finally, in both of the foregoing areas, we plan to apply and use computer graphics as a tool and an aid in various phases of structure determination and in compiling and presenting the results in informative and useful ways.